The invention relates to an ion-laser tube, and more particularly to an ion-laser tube which provides a high output with a discharge of a relatively large current.
In general, the structure of such high output ion-laser tube includes a slender discharge tube made of a ceramic material such as silicon carbide. For such ion-laser tube, the possibility of the accomplishment of a high output with a large discharge current is likely to depend upon the quality of the discharge tube.
The ion-laser tube which employs an ionized gas such as argon and krypton ionized gases is well known in the art. Such ion-laser tube utilizes a laser oscillation caused by transitions of electrons between different energy levels possessed by such atoms of the ionized gas. In order to secure a high output, such ion-laser tube requires a discharge of a large current, typically 30 A or larger, for which a high ion-concentration of the ionized gas is required.
Such gas laser tube is likely to be possessive of a lower efficiency of a laser oscillation. Then, a greater part of a supplied electrical energy by a large discharge current is likely to be converted into a thermal energy and thus be consumed as a thermal energy, although this is undesirable. As a result of those, the slender discharge tube and its vicinity portions are forced to have a heat of a high temperature. Such accumulated heat in the laser tube causes a deformation of the laser tube and a depression of the ability of optical functions and characteristics possessed by the laser tube. Thus, such discharge tube requires a high quality material which is resistive to such high temperature. It is further desirable that the discharge tube and its enclosure members, in which the discharge tube is enclosed, are made of a material having a high heat conductivity so as to eliminate a great deal of the accumulated and unnecessary heat from the laser tube. It is furthermore desirable that the laser tube is possessive of a cooling feature for making an elimination of the undesirable heat. It is yet a further requirement that the slender discharge tube involved in the ion-laser tube is made of a material which is resistive to a high ion-concentration.
In addition, since the discharge tube has an inner wall which is exposed to a high energy plasma gas, or a high energy ionized gas, the inner wall of the discharge tube is subjected to sputtering accomplished by high energy ions and electrons of the plasma gas. Such sputtering causes the quality, or the characteristic of the discharge of the ion-laser tube to substantially be depressed. Then, the discharge tube is required to be made of a resistive material to such sputtering.
In recent years, for complying with the above requirements, it has been considerable to employ silicon carbide (SiC) and aluminium nitride (AlN) as materials of tubular members, for example, the slender discharge tubes and the enclosure members, both of which are involved in the ion-laser tube. The conventional structure of the ion-laser tube will now be described with reference to FIG. 1. The conventional structure of the ion-laser tube includes a slender discharge tube 21 which serves as a discharge tube. The slender discharge tube 21 is made of silicon carbide which is a resistive material to the sputtering caused by a high energy plasma gas. The silicon carbide slender discharge tube 21 is located along a center axis of the ion-laser tube. The silicon carbide slender discharge tube 21 also includes one end with a flange. The silicon carbide slender discharge tube 21 also defines a through hole 2 which serves as a discharge guiding way in which the discharge is occurred.
The silicon carbide slender discharge tube 21 is enclosed by a tubular enclosure member 3 being made of aluminium nitride which has a high heat conductivity. The aluminium nitride tubular enclosure member 3 includes a plurality of gas return holes 4, through which the ion-gas which has been served for discharge is transmitted. The aluminium nitride tubular enclosure member 3 has an inside diameter which corresponds approximately to an outside diameter of the silicon carbide slender discharge tube 21 so that the silicon carbide slender discharge tube 21 is inserted into the aluminium nitride tubular enclosure member 3. The silicon carbide slender discharge tube 21 is connected to the aluminium nitride tubular enclosure member 3 through a frit glass 6 so as to support a high heat conductivity possessed by the aluminium nitride tubular enclosure member 3 thereby resulting in a formation of a combined coaxial tubular member 25 comprising the silicon carbide sledder discharge tube 21 and the aluminium nitride tubular enclosure member 3.
A plurality of such combined coaxial tubular members 25 are connected to one another along the center axis through a frit glass 7 so as to support a high heat conductivity possessed by the aluminium nitride tubular enclosure member 3. The alignment of the combined coaxial tubular members 25 is carried out by using a jig which is not illustrated. The number of the combined coaxial tubular members 25 is variable by matching various requirements. The alignment of the plural combined coaxial tubular members 25 is terminated in borosilicate glass tubes 8. Namely, the alignment of the combined coaxial tubular members 25 is connected at its opposite ends with two of the borosilicate glass tubes 8.
Further, the alignment of the combined coaxial tubular members 25 terminated in the borosilicate glass tubes 8 is sealed at its opposite ends with two metal sealing members 11 respectively. One of the metal sealing members 11 is provided with an anode 9 through an anode side terminal 14. The anode 9 is enclosed by the borosilicate glass tube 8. This metal sealing member 11 further includes an exhaust tube 13 which serves for exhausting an unnecessary discharge gas. The one of the metal sealing members 11 including the anode 9 is located at the side of the one end with the flange of the silicon carbide slender discharge tube 21. Another of the metal sealing members 11 is provided with a cathode 10 through a cathode side terminal 15. The cathode 10 is enclosed by the borosilicate glass tube 8.
Both metal sealing members 11 have slender tubular projective portions which are located along the center axis respectively. Further, the slender tubular projective portions of the metal sealing members 11 are respectively provided with glass members such as Brewster windows 12, each of which has a predetermined locative angle, typically Brewster's angle. After mounting the Brewster windows 12, the ion-laser tube is filled with a predetermined deal of a discharge gas such as the argon gas thereby completing the ion-laser tube.
Since a silicon carbide material is possessive of a high resistivity to sputtering caused by a high energy ion-gas, the employments of the silicon carbide material for the slender discharge tube 21 is likely to be permissive of suppressing but not sufficiently various undesirable affections occurred by sputtering caused by a high energy ion-gas. As an aluminium nitride material is possessive of a high heat conductivity which permits eliminating a great deal of undesirable heat, the employment of the aluminium nitride material for the tubular enclosure member 3 is likely to allow an elimination of an undesirable heat generated by a large current of the discharge. Further, the implementation of cooling by applying a cooling medium on a surface of the ion-laser tube is permissible for the elimination of the unnecessary heat from the laser tube to external portions.
The desirable characteristics possessed by the above materials, or silicon carbide and aluminium nitride are permissive but not sufficiently of rendering the discharge of a large current stable. The characteristics of the output possessed by the conventional ion-laser tube is insufficient to implement a high output generated by a large current flowing the discharge slender tube. The reasons of those are as follows. As described the above, the inner wall of the silicon carbide slender discharge tube 21 is directly exposed to a high energy ionized gas, or plasma gas of a high temperature. Such high energy ionized gas including high energy ions and electrons supplied by a large discharge current, typically 30 A is likely to make sputtering to silicon carbide molecules involved in a surface of the inner wall of the silicon carbide slender discharge tube 21. Silicon carbide molecules which has been subjected to such sputtering are forced to be driven out from the surface of the inner wall of the silicon carbide slender discharge tube 21. After that, the sputtered silicon carbide molecules are likely to be deposited on inner surfaces of the Brewster windows 12. This renders the high output characteristics of the ion-laser tube be substantially depressed.
As a result of an aging test of the ion-laser tube for a high output of 30 A, following matters are observed. The output of the ion-laser tube is slowly reduced due to sputtered silicon carbide molecules. Further, the output of the ion-laser tube sometimes drops out, and thus are rapidly reduced during the operation of the ion-laser tube. The reduction of the output of the ion-laser tube manifests especially in a high output laser tube, but insufficiently in a middle output laser or a low output laser. It is considerable to suppress the substantial reduction of the output of the laser tube due to sputtering to the inner wall of the silicon carbide slender discharge tube 21, which is provided by the large discharge current.
From the aging tests of the output characteristics, it is found that the reduction of the output of the ion-laser tube caused by sputtering provided by the large discharge current is associated with a degree of a roughness in the surface of the inner wall of the silicon carbide slender discharge tube 21. When the degree of the roughness of the inner wall of the silicon carbide slender discharge tube 21 is relatively large, the reduction of the output of the ion-laser tube is also large. In contrast to the above, when the degree of the roughness of the inner wall of the silicon carbide slender discharge tube 21 is relatively small, the reduction of the output of the ion-laser tube is also small. Therefore, in the ion-laser tube involving the silicon carbide slender discharge tube and the aluminium nitride tubular enclosure member, a further improvement of the resistivity to the sputtering to the inner wall of the silicon carbide slender discharge tube 21 requires an uniformity and thus a smaller degree of the roughness in the surface of the inner wall of the silicon carbide slender discharge tube 21. Such improvement of the resistivity of the discharge tube to the sputtering provides the high output ion-laser tube with desirable and excellent output characteristics without reduction or dropping down.